Until recently, the system of Neptune's inner satellites and
ring-arcs had only been observed in direct imaging from the
Voyager~2 spacecraft, limiting our knowledge of this system
to visible wavelengths data. Nearly ten years after the
Voyager fly-by, HST/NICMOS observed the close vicinity of
Neptune at 1.87\mum, a wavelength that corresponds to a
strong methane absorption in the atmosphere of Neptune and
allows the attenuation of the scattered light produced by
the planet. We derived the near-infrared geometric albedo of
the ring-arcs and small moons Proteus, Larissa, Galatea and
Despina, and compared their orbital positions with the
predictions from the 1989 Voyager observations. The surfaces
of the inner satellites of Neptune appear to be coated with
dark, neutral material, with albedoes ranging from 0.077
(Proteus) to 0.033 (Despina) and their orbital position was
found to be within the prediction errors of the Voyager
measurements. The material located inside the ring-arcs of
Neptune also displays a low-neutral reflectance (p1.87
\mu m ~0.055) and the HST/NICMOS measurement of the
mean orbital motion of the ring-arcs shows that their
confinement cannot be entirely explained by resonances
produced by the nearby satellite Galatea (Nature, 400,
733-735).

This work was performed at the Jet Propulsion Laboratory,
Caltech, under contract with the National Aeronautics and
Space Administration, and is supported by NASA grant
NAG5-3042.

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